1. Field of the Invention
The present invention relates to methods and devices for processing waste, especially radioactive, toxic, industrial and household waste generated from factories, nuclear power plants, hospitals, institutions and the like. More particularly, the present invention relates to the treatment of wastes from solid and liquid, including both aqueous and nonaqueous, wastes streams to form a stable, final glass waste product.
2. Discussion of Background
Economic and regulatory factors require nuclear power utilities and other generators of radioactive waste to develop and evaluate new technologies and methodologies for improving safety and reducing the costs of operations. Also, reducing the volume of waste generated and improving the stability of the disposed waste is of prime interest within our increasingly environmental-conscious society. Improvements in waste processing operations and procedures can significantly reduce waste management costs, waste volume, and the concern associated with storage and permanent disposal of the final waste.
Additionally, existing legislation may require all power plants to store on-site the waste each plant generates if centralized storage or disposal facilities are not available. Thus, improvements in waste processing systems should include not only significant reductions in the volume of the final waste form but also the capability of identifying and separating the waste from each generator so that waste can be returned to the generator for storage.
Nuclear power plants, which produce much of the radioactive waste, generate a plurality of waste types typically broken down into three classifications: "dry active waste" (DAW), "wet waste" or ion exchange resins and "liquid waste." Dry active waste includes paper, wood, metal scraps, plastic sheeting, clothing and the like. Currently, dry active waste is processed by low and high density compaction, with compaction ratios of approximately 2:1 to 6:1, depending on its particular composition and the force exerted. Some forms of DAW are currently incinerated with a volume reduction of approximately 50:1.
Wet waste includes ion exchange resins, typically in granular or powdered form. Wet waste is currently processed by dewatering (drying) to take out interstitial or free water. Usually, drying does not necessarily include removing water from the resin bead itself.
Liquid waste includes organic waste (oils, chemical solutions), which is combustible, and inorganic waste such as aqueous wastes and sludges, inorganic acids, and solutions of boron, NaOH and the like. Organic wastes are currently incinerated or stabilized. Inorganic waste, mostly comprised of aqueous salt solutions, is currently being processed by demineralization, ion exchange, membrane technology and evaporation, all of which are well known in the art of waste processing. Also, aqueous waste is processed by evaporator/dryers to yield concentrated and/or dried, solid waste.
Numerous processing methods are known for treating and processing waste generated from power plants and the like, including radioactive wastes generated from nuclear power plants. For example, Bardot et al, in U.S. Pat. No. 4,925,566, describe the use of ultrafiltration, hyperfiltration and demineralization for radioactive liquid elements.
Also, the notion of ion exchange and the use of ion exchange resins for radioactive waste processing is well known, as described in U.S. Pat. Nos. 3,520,805, issued to Ryan, and 4,415,457, issued to Shirosaki et al. Ryan describes filtration through ion exchange resin-coated fibers. Shirosaki et al absorb ions in power plant filter backwash onto an ion exchange resin.
Several U.S. patents combine additional waste processing methods with the use of ion exchange resins. These patents include U.S. Pat. Nos. 3,773,177, issued to Queiser et al, and 5,158,674, issued to Kikuchi et al. Queiser et al follow the use of ion exchange resins with filtration and drying processes. Similarly, Kikuchi et al treat radioactive liquid wastes using membranes to concentrate the wastes, filtration of oils using active silica, and then incineration of the flammable solids on the active silica. Also, in Macedo et al (U.S. Pat. No. 4,737,316), contaminated liquid is purified by passing it through an ion exchange resin then "sintering" the resin.
Another procedure known for use in processing radioactive waste is vitrification, that is, the incorporation of the inorganic portion of the waste into a stable, glass matrix having radioactive elements as part of the glass structure. Vitrification has been studied for decades as a way of stabilizing high level radioactive waste, and a number of patents exist that relate thereto. However, more recently, vitrification has been used with other types of radioactive wastes. For instance, Macedo et al (U.S. Pat. No. 4,737,316) state in their specification that it is well known to form borosilicate glass from the processing of ion exchange resin and glass frit.
Incineration is used to reduce the volume of radioactive waste but, because the ash produced from combusting the waste contains radioactive material, further processing of the ash is required to stabilize it.
Despite the number of waste processing procedures known for use with hazardous or radioactive wastes from power plants and the like, there exists a need for an effective process system that significantly reduces the volume of all types of waste from nuclear power plants, and produces a stable, final waste product that is easily manageable for storage, transporting, disposal and the like.